Cassini sees Saturn rings oscillate like mini-galaxy (w/ Video)

November 1, 2010

NASA's Cassini spacecraft captured this image of a small object in the outer portion of Saturn's B ring casting a shadow on the rings as Saturn approached its August 2009 equinox. Image credit: NASA/JPL-Caltech/SSI

(PhysOrg.com) -- Scientists believe they finally understand why one of the most dynamic regions in Saturn's rings has such an irregular and varying shape, thanks to images captured by NASA's Cassini spacecraft. And the answer, published online today in the Astronomical Journal, is this: The rings are behaving like a miniature version of our own Milky Way galaxy.

This new insight, garnered from images of Saturn's most massive ring, the B ring, may answer another long-standing question: What causes the bewildering variety of structures seen throughout the very densest regions of Saturn's rings?

Another finding from new images of the B ring's outer edge was the presence of at least two perturbed regions, including a long arc of narrow, shadow-casting peaks as high as 3.5 kilometers (2 miles) above the ring plane. The areas are likely populated with small moons that might have migrated across the outer part of the B ring in the past and got trapped in a zone affected by the moon Mimas' gravity. This process is commonly believed to have configured the present-day solar system.

"We have found what we hoped we'd find when we set out on this journey with Cassini nearly 13 years ago: visibility into the mechanisms that have sculpted not only Saturn's rings, but celestial disks of a far grander scale, from solar systems, like our own, all the way to the giant spiral galaxies," said Carolyn Porco, co-author on the new paper and Cassini imaging team lead, based at the Space Science Institute, Boulder, Colo.

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The outer edge of Saturn's B ring exhibits an unexpected feature in this movie made from images captured by Cassini. It is apparent in the movie that the outer B ring edge location varies with time. Credit: NASA/JPL-Caltech/SSI

Since NASA's Voyager spacecraft flew by Saturn in 1980 and 1981, scientists have known that the outer edge of the planet's B ring was shaped like a rotating, flattened football by the gravitational perturbations of Mimas. But it was clear, even in Voyager's findings, that the outer B ring's behavior was far more complex than anything Mimas alone might do.

Now, analysis of thousands of Cassini images of the B ring taken over a four-year period has revealed the source of most of the complexity: at least three additional, independently rotating wave patterns, or oscillations, that distort the B ring's edge. These oscillations, with one, two or three lobes, are not created by any moons. They have instead spontaneously arisen, in part because the ring is dense enough, and the B ring edge is sharp enough, for waves to grow on their own and then reflect at the edge.

"These oscillations exist for the same reason that guitar strings have natural modes of oscillation, which can be excited when plucked or otherwise disturbed," said Joseph Spitale, lead author on today's article and an imaging team associate at the Space Science Institute. "The ring, too, has its own natural oscillation frequencies, and that's what we're observing."

Astronomers believe such "self-excited" oscillations exist in other disk systems, like spiral disk galaxies and proto-planetary disks found around nearby stars, but they have not been able to directly confirm their existence. The new observations confirm the first large-scale wave oscillations of this type in a broad disk of material anywhere in nature.

Self-excited waves on small, 100-meter (300-foot) scales have been previously observed by Cassini instruments in a few dense ring regions and have been attributed to a process called "viscous overstability." In that process, the ring particles' small, random motions feed energy into a wave and cause it to grow. The new results confirm a Voyager-era predication that this same process can explain all the puzzling chaotic waveforms found in Saturn's densest rings, from tens of meters up to hundreds of kilometers wide.

"Normally viscosity, or resistance to flow, damps waves -- the way sound waves traveling through the air would die out," said Peter Goldreich, a planetary ring theorist at the California Institute of Technology in Pasadena. "But the new findings show that, in the densest parts of Saturn's rings, viscosity actually amplifies waves, explaining mysterious grooves first seen in images taken by the Voyager spacecraft."

The two perturbed B ring regions found orbiting within Mimas' zone of influence stretch along arcs up to 20,000 kilometers (12,000 miles) long. The longest one was first seen last year when the sun's low angle on the ring plane betrayed the existence of a series of tall structures through their long, spiky shadows. The small moons disturbing the material are probably hundreds of meters to possibly a kilometer or more in size.

Cassini scientists may have identified the source of one of Saturn's more mysterious rings. Saturn's G ring likely is produced by relatively large, icy particles that reside within a bright arc on the ring's inner edge.

The Cassini spacecraft has obtained the most detailed look ever at Saturn's rings, including the B ring, which has eluded previous robotic explorers. Its structure seems remarkably different from its two neighbors, rings ...

(PhysOrg.com) -- NASA's Cassini spacecraft has found within Saturn's G ring an embedded moonlet that appears as a faint, moving pinprick of light. Scientists believe it is a main source of the G ring and its single ring arc.

Scientists examining Saturn's contorted F ring, which has baffled them since its discovery, have found one small body, possibly two, orbiting in the F ring region, and a ring of material associated with Saturn's moon Atlas.

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10 comments

Raises the question of how long these resonance oscillations can/will last? Where would the energy comes from to last 4 billion years?Where do the rings themselves comes from in the first place since normal accretion theory does not / cannot account for their existence [ why don't OTHER planets have rings as broad as these? ]

How would those "mysterious" grooves arise from simple resonance? Interesting to note that the viscosity theory is now being reversed. Will watch this space with interest - pun intended.

The rings of Saturn have nothing to do with gravity. The belief that gravity is the force shaping the rings is why those studying them have all these issues. Clue: Saturn's magnetic field is exactly aligned with it's rotational axis. This is why Saturn's rings are so pronounced. Paper on this coming soon, and these MAGNETIC FIELD effects have dupicated in the lab. Once you see the lab tests I have seen, all these bizarre features in Saturn's rings, hexagonal pole pattern, and bizarre orbital behaviors become quite easy to understand. All this appeared in one physical (Not computer sim) model of Saturn's magnetic fields that I witness in person. Sorry but the conclusions they reach in this paper are plain wrong. Anomalies are clues that your basic understanding is wrong, not a reason to invent another complicated explanation.

The rings of Saturn have nothing to do with gravity. The belief that gravity is the force shaping the rings is why those studying them have all these issues. Clue: Saturn's magnetic field is exactly aligned with it's rotational axis. This is why Saturn's rings are so pronounced. Paper on this coming soon, and these MAGNETIC FIELD effects have dupicated in the lab. Once you see the lab tests I have seen, all these bizarre features in Saturn's rings, hexagonal pole pattern, and bizarre orbital behaviors become quite easy to understand. All this appeared in one physical (Not computer sim) model of Saturn's magnetic fields that I witness in person. Sorry but the conclusions they reach in this paper are plain wrong. Anomalies are clues that your basic understanding is wrong, not a reason to invent another complicated explanation.

Skeptic - Are you sure A2G is Zephyr - it just doesn't look the same to me. Kevin is of course himself.

The blast from the sun should be giving a charge to Saturns rings and static charges (if so) would make a lot of interesting patterns. BUt so too for gravitational attraction between the ring and and all objects within the ring. Any perturbation would create an area of increased gravity attraction and if charged there would be an increase in repulsion. Indications are that one or the other or both are active.

I don't know which but I am sure the observers of this phenomena would try them all out to see which fits best.

Maybe I missed something, but I hadn't heard that it was confirmed/supported that the rings were long term (4bYr) phenomena. I recall theories that these may be short-lived millions or less of years phenomena...

So an argument that since their formation theory doesn't fit a 4Byr life is not relevant.

Nope, if you consider the tidal effects a product of common gravity. There is interesting point, though, the path of galactic arms can be predicted with epicycle model, which was quite popular before Galileo.

The large object is, the more it becomes similar to dual model - and this is something, which has a deep meaning in more general theory. These multiparticle emergent phenomena are actually artifacts of quantum mechanics, which described the space-time curved from extrinsic perspective, i.e. in similar way, like the epicycle model is describing solar system.

BTW note that the rectangular shape of Milky way brings the relevance of swastika, i.e. ancient archetypal symbol for "ring of suns", i.e. the galaxy. It seems, ancient civilizations knew about all these connections - we are just revealing them again.

BTW The average size of ice particles in Saturn rings is of evolutionary nature and it corresponds the wavelength of CMB radiation. Larger particle would coalesce with their gravity, whereas these smaller ones would evaporate into thermal radiation. The CMB wavelength is just the size, where all these objects remain as stable, as possible - so it forms the dimensional scale of human observers, too. It's the dimensional scale of maximal complexity, where relativistic phenomena (gravity in particular) are just compensated with these quantum mechanic ones (i.e. pressure of radiation in particular).

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